UK investigators finger emergency beacon for 787 Heathrow fire

Fixing the problem an hour-long job, says Boeing

The initial accident report into the Boeing 787 that caught fire at London's Heathrow airport last week has concluded that the fault likely lies with the aircraft's emergency location beacon, and it recommends disconnecting it as an interim measure.

The world's third-busiest airport was shut down for over an hour on Friday after the tail section of the Queen of Sheba, run by Ethiopian Airlines, caught fire on its stand while unoccupied. The UK Air Accidents Investigation Branch (AAIB) report says firemen were at the plane within a minute of the fire being reported and used water to put out the fire after the on-board halon extinguisher proved insufficient.

The investigators found the hottest part of the fire occurred near the emergency locator transmitter (ELT) and its associated system wiring. The ELT, manufactured by Honeywell, is a beacon designed to automatically broadcast the aircraft's location after a crash and is powered by lithium-manganese dioxide batteries that differ chemically from those which caused Boeing's previous problems.

The battery cells did show disruption, but the investigators can't determine if this was because of the fire or as a result of battery ignition, or if they suffered a short-circuit in the system's wiring. As a precaution, the AAIB recommends airlines "initiate action for making inert" all ELTs of that design, of which there are 6,000 in circulation, until a safety review has been carried out.

"As a safety-first focused company, we support the AAIB's proposal and will offer assistance to Boeing and the airlines if needed. The investigation continues, and it's premature to jump to conclusions," Honeywell told El Reg in a statement. "Temporarily addressing the ELTs on Boeing 787s as a precautionary measure is prudent."

A Boeing spokesman told The Register that the operation to remove the ELT can be accomplished in an hour by an aircraft engineer and that the beacons are not a requirement for US air travel, although some countries do demand them for flights in their airspace.

"We are confident the 787 is safe and we stand behind its overall integrity," the company said in a statement.

But some in the industry are expressing concern that the official explanation doesn’t quite add up. Aviation journalist Christine Negroni reports that the Teflon wiring used to save weight (and thus fuel) in the 787 is excessively brittle and engineers warn "Don't look at it too hard or you'll break it."

"Somebody made the decision to use it," Negroni was told of Boeing and the French company Labinal, which specializes in electrical wiring used in the 787. "It will come and bite Boeing on the ass. We have a lot of problems with this airplane because of the wiring."

Negroni also pointed out that the amount of electronics in the aircraft and the composite panels used in the cabin's construction reportedly make it overheat fairly easily. The AAIB report states that the Queen of Sheba was connected to a mains power supply but that power was not switched on at the time.

The AAIB report also said that the ELT beacon should be removed in cargo aircraft, since they "do not typically carry the means of fire detection or suppression in the space above the cabin ceilings." An on-board fire on a transoceanic cargo flight ranks high among a pilot's worst nightmares, Patrick Smith, veteran aviator and author of the Ask the Pilotblog told The Register.

"It remains to be seen what caused the fire," he said. "All aircraft have teething problems but standards are a lot higher than they used to be, but it's a bit of a black eye for Boeing." ®